The invention relates to an apparatus for the reproduction of optical sound recordings, which has an optoelectronic converter device for the optical scanning of an optical sound track, which outputs a digital image signal of the scanned optical sound track at an output, and which contains a device for buffer-storing the image signal output by the converter device. Furthermore, the invention relates to a method for the reproduction of optical sound recordings, in particular optical sound recordings in which the sound information is recorded as a double variable-area track on film.
In the case of 35 mm cinema films, the sound information is recorded on an optical sound track which is located between image information and lateral perforation holes. For the reproduction of the sound information, the film is transported at a speed of 24 frames per second. While the film is being transported, a light beam illuminates the optical sound track. The light beam is modulated by transparency differences in the scanned optical sound track and directed onto a light-sensitive sensor. For loudspeaker reproduction, the analogue sound signal output by the light-sensitive sensor is amplified.
There are various optical sound tracks. In the case of the so-called variable-density track, the transparency of the optical sound track is proportional to the recorded modulation amplitude. In the case of the so-called double variable-area track, the width of the clear area is proportional to the modulation amplitude of the sound signal.
Older films that are frequently used often exhibit two types of error: one type involves dirt and dust on the surface of the film; the other type involves scratches in the running direction of the film, so-called running scratches, which are caused by mechanical contact of the film guiding elements with the film surface. Optical sound tracks are particularly sensitive to disturbances caused by dirt and scratches, the number of which rises with the number of times that the film copy is projected. Distortions of speech sibilants, a so-called thunder effect, can arise as a result of scattered light effects of the variable-area track.
In order to restore old cinema films, nowadays the image part is copied onto a new film carrier and the optical sound track is transferred to a magnetic film in single-track fashion in order to prevent the sound tracks that are often scratched and in part disturbed by dirt from being transferred to the new film carrier as a result of optical copying of the optical sound tracks. Furthermore, sound post-processing with electronic filters and manual processing is used in an attempt to remove clicks and crackling from the original sound.
DE 197 29 201 A1 has already described a film scanner with a device for scanning optical sound tracks on a tape-type carrier, in the case of which the sound information is scanned perpendicularly to the direction of movement of the carrier by an opto/electronic converter device. The opto/electronic converter device scans the sound information line by line in order to generate samples for a digital two-dimensional filtering. In this case, the optical sound tracks can be scanned by a CCD line sensor or by a light spot for the control of a photosensor, which light spot is directed transversely over the sound tracks.
U.S. Pat. No. 4,124,784 A discloses an apparatus for the reproduction of optical sound recordings in which the edge of the optical sound track is scanned. An analogue scanning signal filtered in a suitable manner forms the basis for the signal processing. The purpose of the apparatus is to improve the sound signal and to reduce noise.
DE 19 737 570 A discloses an archiving system for cinematographic film material with a film scanner. The film scanner optically scans the image information and an image sound track. The image data are stored in digitized form without further processing. Sound and image signals are reproduced as separate data signals.